1. Field of the Invention
This invention relates generally to polymer-modified hydraulic cements, and more specifically to polymer latex-modified cement compositions for use in adverse environmental conditions.
2. Brief Description of the Prior Art
Portland cement concrete is widely used in modern construction, being used in a multitude of applications, ranging from forming walls and floors to casting water and sewer pipes and erecting storage tanks. Although it has high compressive strength, and is relatively inexpensive and durable, Portland cement concrete does have a number of disadvantages in various applications. For example, it has poor colorability and tends to effloresce, and has poor resistance to aqueous acids. These properties, in particular the poor aqueous acid resistance, make it desirable to protect Portland cement concrete with a chemically resistant coating or overlay in many applications.
Thick coatings (often referred to as a "topping," "lining," or "overlay" when greater than about 0.25 cm thick) are preferred for long term resistance to chemicals, in applications where significant abrasion is encountered, or where coarse aggregate must be added to provide slip resistance.
Two classes of compositions are in use for forming protective coatings for Portland cement concrete. The first class consists of "polymer concrete" compositions which include reactive organic liquid materials which solidify under cure conditions. The second class is formed of polymer-modified hydraulic cements. Conventional solvent-based organic coating compositions tend not to be used because solvent is retained in thick films, resulting in one cure times and long-term solvent release. Hydraulic cements without polymer modifiers are not useful because they tend to show poor adhesion and chemical resistance, and lack strength.
Polymer concrete compositions typically comprise about 13 percent by weight organic material when formulated for use at about 0.636 cm thickness, and are typically formulated using a binder made up of an epoxy resin and an amine curing agent for the epoxy. While this type of binder can provide reasonable cure and chemical resistance at low cost, cracking and delamination are recognized as problems with epoxy/amine polymer concrete overlays, in particular outdoors. Ultraviolet degradation of epoxy/amine polymer concrete is also recognized as a problem. Even for indoor applications, cracking and desalination can be encountered where the overlays are exposed to changes in temperature such as in food or beverage plants, or pharmaceutical plants, where steam or hot water is used to clean floors.
Polymer-modified hydraulic cements typically employ a lower level of organic materials than polymer concrete, resulting in a coefficient of thermal expansion similar to the Portland cement concrete, and lower materials costs. While polymer-modified hydraulic cements tend to give good resistance to cracking and delamination, their chemical resistance tends to be poorer than desired, in particular their resistance to aqueous acids. Because a lower level of organic materials is generally employed in polymer-modified hydraulic cements than in polymer concretes, and because organic materials are generally more costly as a class than inorganic materials, polymer-modified hydraulic cements are often less costly than polymer concretes.
There is a need for a polymer-modified cementitious composition, and especially a polymer-modified cementitious composition including hydraulic cement, which can be used as a coating or overlay composition for Portland cement concrete, which has a relatively low cost, and good resistance to chemicals, in particular good resistance to aqueous acids.
In addition to relatively high costs, polymer concrete compositions may have a number of other drawbacks such as unacceptable volatility, flammability and toxicity. They may require special equipment to achieve cure, and may require on-site mixing of multiple components, and concomitantly, multiple packages for shipment.
There is a need for a coating composition for Portland cement concrete which requires a minimum of components to be separately packaged and shipped, and mixed together with other materials at the site of the application.
Epoxidized polymeric materials have long been used for modifying hydraulic cements including Portland cement. For example, U.S. Pat. No. 3,449,278 discloses improving concrete strength through use of an emulsified epoxy resin and an amine, the epoxy resin including adducts of epoxide with an excess of styrenated amidoamine, providing good water dispersibility. Another polymeric material used for this purpose has been aqueous latex. Combinations of the two have also been known. For example, U.S. Pat. No. 3,240,736 discloses an aqueous binder or mortar comprising 20-85 percent by weight hydraulic cement, 2-25 percent polymer latex as a plasticizer, and 10-50 percent ambient curing resin selected from epoxide, polyurethane, polyester and silicone. Water is added to cure the hydraulic cement; and a curing agent for the resin is used: polyamide for the epoxide resin, an amine for the polyurethane, a peroxide for the polyester, and a low molecular weight polyamide for the silicone. Similar compositions without hydraulic cement are disclosed for similar applications in U.S. Pat. No. 3,316,187, in which phenolic microballoons are substituted for the hydraulic cement of the '736 patent. U.S. Pat. No. 3,822,229 discloses a plastic aqueous binder mixture consisting essentially of 20-85 percent by weight hydraulic cement, 15-50 percent liquid epoxy resin and curing agent, and 2-25 percent of polymeric latex solids. A special plasticizing agent is disclosed, the plasticizing agent including a film forming copolymer and a carbocyclic compound with two vicinal carboxy groups, such as phthalic acid. The latex can be advantageously dried and packaged with the cement, reducing the number of components and packages required. Soviet patent 883114-A discloses a corrosion-resistant industrial flooring composition including a synthetic rubber latex, an epoxydimethylhydantoin resin, marshalite and an amino-phenol epoxy curing agent.
Combinations o latex polymers and epoxy resins are also known in the adhesive arts. For example, U.S. Pat. No. 4,588,757 discloses a method of synthesizing an emulsion polymer having a glass transition temperature of from about -10.degree. C. to -50.degree. C. in the presence of an epoxy resin. The resulting material is mixed with an aqueous emulsion of an amine-functional resin to give an adhesive for bonding plastic substrates. U.S. Pat. No. 4,510,274 discloses an adhesive composition including an ethylene/vinyl acetate/acid/acrylamide latex polymer, an epoxy resin, and an amine for laminating polyolefin films. U.S. Pat. No. 4,532,273 discloses an adhesive composition for automotive applications. The adhesive includes a latex polymer, an epoxy resin, a tackifier and an amine curing agent, the latex being polymerized from monomer including an adduct of epichlorohydrin and a tertiary amine ester of (meth)acrylic acid. U.S. Pat. No. 3,578,548 discloses the use of an epoxy resin as a transient tackifier for latex-based pressure sensitive adhesives. An adduct of epoxy resin and diethlyenetriamine (DETA) is use to cure the transient tackifier. Soviet patent 421559-A discloses a composition useful as an adhesive for industrial flooring, the composition including 19-34 percent by weight epoxy resin, 1-12 percent liquid latex, 2-10 percent polyethylenepolyamine hardener, 40-70 percent filler, and 7-14 percent tetraethoxysilane. European patent application 245012 discloses a two-part composition, the first part including an oil-soluble catalyst for carboxyl/epoxy cure and an epoxy emulsion, the second part including a butadiene-styrene latex polymer and a water-soluble amine. When mixed the two parts provide a long-pot life epoxy/carboxylated latex having a quick film cure. Compositions including latex polymer, epoxy resin, and epoxy curing agents other than catalysts for epoxy-carboxyl are disclosed, for example, in U.S. Pat. Nos. 4,520,107, 4,522,962, 4,510,274, 4,427,804, 4,485,200, 4,367,298, 4,342,843, 4,377,433, 4,222,981, and 3,859,239, Soviet patent 1014879-A, Japanese unexamined patent publications (Kokai) 58-007467, 53-096942, and 50-111129, and Canadian patent 1,043,486.
Combinations of latex polymers and epoxies have also been disclosed in other arts. For example, U.S. Pat. No. 4,049,869 discloses a composition including a high-acid acrylic latex (e.g. 14 percent acrylic acid), an ultraviolet absorber, and a crosslinking agent, for use in preserving porous inorganic substrates. The crosslinking agent can be epoxy resin, and polyethyleneimine or melamine resin can be optionally included.
Organosilanes are known for use in treating cementitious surfaces to improve adhesion. U.S. Pat. No. 4,626,567 discloses a water-resistant acrylic latex sealant composition which includes an organoaminosilane, as well as a small amount of silica, such as a fumed silica, which cooperates with the silane to provide enhanced adhesive properties. U.S. Pat. No. 4,518,653 discloses a glass fiber treatment employing a composition including an epoxy resin, polyvinyl pyrrolidone, an emulsifier or dispersible nontacky film-forming polymer, such as a bisphenol polyester resin, and methacryloxyalkytrialkoxy silane.
While some compositions are known to provide specific properties which are desirable for Portland cement concrete overlays, such as long pot life, rapid early strength development, high ultimate strength, good resistance to chemicals and delamination by thermal shock, and two-component packaging and mixing, no single prior composition is known to provide a desirable balance of all these properties. There is a need for a coating or mortar mix composition, including a hydraulic cement such as Portland cement, which can be packaged as a two component system, and subsequently stored and later transported to the site of application, where the two components can be mixed together with water to provide a coating composition with good pot life, but which rapidly develops strength after application, ultimately providing a coating with good chemical and thermal shock resistance for a Portland cement concrete or metal substance.